Giedo van der Garde believes that Caterham still has some work to do with finding rear grip with its new car despite a positive first day of 2013 Formula 1 testing.
The Dutchman, who will make his F1 debut for Caterham this year was entrusted with the new CT03 for its first day of running.
He completed 64 laps in the new car, lapping 3.054 seconds off pacesetter Mark Webber's Red Bull.
Asked by AUTOSPORT about the overall impression of the car, he replied: "I think positive.
"The front end is a bit stronger than last year, which suits me better, and this was also a target that [ex-Caterham driver] Heikki [Kovalainen] was working on a lot.
"The rear is a little issue at the moment. It's a little loose, but for the first day, I was quite happy."
Van der Garde is scheduled to continue in the car on Wednesday before handing over to team-mate Charles Pic for the final two days of the Jerez test.
He accepts that the team still has some way to go with understanding the 2013 Pirelli tyres and that this will be an area to focus on during Wednesday's track time.
"It's responding quite well but the biggest thing is that we still need to get a handle on the tyres because it's quite different from last year," he said.
"We'll see what we can do tomorrow, but the feeling with the car is quite positive."
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